This invention relates to roller mills and more particularly to a corrugated pipe forming machine having a corrugating roller mill of the type having upper and lower opposed corrugating rollers for manufacturing the pipe from flat sheet metal.
Corrugating pipe is presently in wide use because of its relatively high strength and low cost. Since such pipe is normally buried its appearance is of secondary consideration and most tolerances of the pipe are loose which further contributes to the economy of such pipe.
A stringent requirement of such pipe, however, is that it be structurally sound. Since the pipe is almost always formed by helically winding a continuous length of corrugated sheet structural soundness usually hinges upon the formation of a high strength seam as the sheet is helically wound. Seams can be formed by welding the edges of the metal or by forming a mechanical interlock, also called a Pittsburgh lock. The mechanical lock is formed by first rolling a longitudinally extending edge lip on the corrugated sheet which extends generally perpendicular to the remainder of the sheet. As the sheet is helically wound, the edge lips are overlapped and folded over to form the lock. Tight tolerances in the dimensioning of the lip must be maintained. The width of the lips must be within plus or minus one thirty-second of an inch and both lips must be of equal width. Since the lips are formed by laterally disposed edge forming rolls the sheet must therefore be precisely centered relative to such rolls. Moreover, the overall width of the sheet must be closely controlled to maintain the desired lip dimensions and tolerances.
Given this requirement and the need for multiple corrugating rolls, in which each corrugating station is defined by a pair of opposed rollers which progressively form the corrugations from the center towards the sheet edges, the prior art has developed so-called line formers in which the corrugating stations are separate and independent so that each station must be adjusted individually. Such individual adjustment enables one to precisely align the corrugations in the sheet with the edges and to generally produce a high quality corrugated sheet. This is of great importance when the corrugated sheet is used for covering roofs, sidewalls, etc. It is relatively insignificant when the corrugated sheet is subsequently deformed, as on a helical corrugated pipe rolling machine since misalignments of individual sheet corrugations relative to each other or relative to the sheet edges become undetectable due to the general stretching and deformation of the sheet when it is wound. The overall sheet width and/or the absolute and relative dimensions of the edge lips, however are of the utmost importance and must fall within specified dimensions and tolerances.
Prior art corrugated pipe forming machines apparently never recognized this distinction, or gave no importance to it, and employed line formers constructed of a plurality of independent corrugating stations. Since the effective width of the sheet, and therewith the effective dimensions and tolerances of the edge lips is a function of and can be varied with variations in the depth of the corrugations, any adjustment required an adjustment of all corrugating stations. This was time-consuming and required highly skilled, and therefore, expensive labor. Moreover, since the independent corrugating stations are spaced relatively far apart, a substantial length of sheet material must be run through the corrugator before the final dimension can be taken and before it can be determined whether or not the adjustments were sufficient or accurate. If not, the length of sheet metal just run through the corrugator is wasted and must be discarded. In prior art pipe rolling machines present in extensive use, wastage could amount to as much as 24 feet for each dimension check.
Thus, it may be summarized that prior art corrugated pipe forming machines employed sheet metal corrugators which yielded high accuracy in an area where accuracy is of little importance, namely, the alignment of the corrugations relative to each other and relative to the sheet edges. However, such corrugators made it difficult, time-consuming, and therefore, expensive to attain and maintain accuracy where it counts, namely, in the dimensioning and the tolerances of the edge lips which subsequently form the continuous pipe seam.
The corrugators employed with prior art pipe rolling machines have included at least three additional specific disadvantages.
A first disadvantage of the prior art is that each of the opposed rollers has heretofore been mounted on journals, which journals are individually adjustable. It is known that corrugation requires precise and equal adjustment between sequential corrugating rollers. The individually adjustable rollers of the prior art make such adjustment difficult, at best, and only capable of achievement by mechanics of relatively high skill.
Moreover, this problem is often compounded by the sheet metal or skelp being processed. Varying thickness of skelp found either from roll to roll or even in different segments of the same roll requires different adjustments. Where individual adjustment of individual rollers is required, loss of time and loss of unsatisfactory corrugated skelp results.
Second, the drive of the sequential rollers has presented a problem. The fact that opposed rollers must be adjustable towards and away from one another has compounded this problem. Specifically, either chain drives or idler gear drives between adjacent rollers have been used.
Where chain drives have been used, the chain is commonly wound so as to drive each and every roller. The result is that the chain of the drive must be of a thickness to transmit the power to drive all rollers. Extreme chain bulk and cost results. Moreover, increased sprocket size is frequently required to reduce chain thickness to tolerable limits. The sprockets which, of necessity, must be in line, are further spaced apart. The individually powered rollers must be further apart resulting in a longer mill. Increased machine length results in increased difficulty of adjustment and increased scrap loss where insufficiently corrugated skelp is produced -- especially during machine adjustment.
Moreover, idler gear drives have extreme disadvantages. Primarily, idler gears are expensive mechanisms which complicate machinery in which they are used as to numbers of moving parts and maintenance. Additionally, and more seriously, the number of rollers which can be driven from an individual power source through an idler gear drive chain is limited. Where more than four rollers are all driven off of the same torsional power input through idler gears, gear bulk -- either in length or diameter -- must be increased dramatically.
Finally, such roller mills have, in the past, included corrugated rollers which comprise short and discrete cylindrical sleeves which are placed as segments over underlying rigid and rotating shafts. The corrugating rollers at the sleeve segments provide no part of the considerable rigidity required for corrugation by opposing rollers. As a result, the rotating and underlying shafts and journals have to be of a relatively large diameter. Correspondingly, the discrete roller segments for corrugation have to be of even a larger diameter. As a consequence, at least the thickness and the length of such machines must be of relatively large dimension with corresponding increased cost of machine fabrication and operation.